Vulcanized fibre



June I5, E965 H. M PHILLIPS 3,189,515

FIBRE Fed Oct- 5. 1961 REACTIVE PAPER SHEETS LESS REACTIVE KRAFT PAPER SHEETS INVENTOR. HOWARD M. PHILLIPS 'BYQM MM ATTORNEYS United States Patent Oliice 3,189,5154 Patented .lune 15, 1965 3,189,515 VULCANLZED FIBRE Howard M. Phillips, Philadelphia, Pa., assigner to Taylor Corporation, a corporation of Delaware Filed Get. 5, 1961, Ser. No. 143,195

8 Claims. (Cl. 2161-269) This invention relates to vulcanized libre and more particularly .to an improved method of manufacturing vulcanized fibre; the use of cellulosic raw materials from many prime sources; and a substantial reduction in raw material costs.

Vulcanized libre is a regenerated cellulose product which has been known to the art for a great many years. It is made by passing layers of paper through a bath of zinc chloride or sulphuric acid, plying the saturated sheets together, leaching out the zinc chloride or sulfuric acid, and drying the thus formed product. The traditional method was limited to the use of paper with the same pulp constituent which was prepared to react when saturated with zinc chloride or sulfuric acid to the degree necessary to produce the type of vulcanized bre desired. The nished properties vary from a dense, fused material with rather brittle characteristics, to a soft, papery, weakly-bonded material with fair flexibility. The cost of processing the raw material is high and the control of the desired end properties of the finished vulcanized libre by the prior art method is uncertain and costly.

In accordance with this invention, vulcanized bre of any commercial grade can be made with facility and costs are substantially lower and cleanliness of product far superior than the conventional vulcanized libre method. Surprisingly, it has been found that kraft paper, which had been previously rejected by the industry, as valueless in this process because of its relative inertness, can be employed as a substantial portion of the total raw material for the paper used to produce vulcanized libre. Further, the process of this invention lends itself to ready modification of the properties of the end product in a controlled manner.

These and other objects of this invention will be further clarified in the following description read in conjunction.

with the drawings in which:

FIGURE l is a schematic elevation of known apparatus` suitable for carrying out the production of the libreboard of this invention; and

FIGURE 2 is a perspective View of an embodiment of the breboard of this invention.

The conventional vulcanized libre making apparatus 2 has a plurality of paper storage rolls 4, 6, 8, and 12 from which are led respectively paper sheets 14, 16, 1S, 2l) and 22, these sheets are led downwardly into tank 24 containing a 70 Baume solution of zinc chloride indicated at 26, each sheet being guided first by rollers Z8 and secondly by rollers 30. The sheets are then plied together by passing around an upper roll 32 and a lower roll 34 from which the plied sheet indicated at 36 is led through a series of leaching tanks 40, 42, 44 and 46, tanks 40, 42, and 44 containing gradually decreasing concentrations of zinc chloride solution and tank 46 containing water. A series of rollers 4S are provided for the guidance of sheet 36 through the leaching tanks. Sheet 36 is then conveyed over heated drier rolls 50, S2, 54 and 56 and thence around a series of calendering rolls indicated at 58 and finally is wound up on storage reel 60.

As described above, the apparatus and method of making wlcanized libre is well known to the art and hence need not be gone into iu any further detail here. Indeed the apparatus of the prior art is employed in making the vulcanized -bre of this invention.

The conventional method is based on the utilization of the same paper to form any one type of vulcanized fibre.

In contrast the method of this invention differs from the prior art in that it employs two different types of paper sheets, namely, a plurality of relatively reactive and relatively unreactive paper sheets to form the vulcanized fibre in the desired thickness. A relatively reactive paper sheet is located between every relatively unreactive paper sheet. The cellulose of the relatively reactive paper sheet is gelatinized by a chemical solution which serves as a bond between the relatively unreactive sheets. It is to be noted that the cellulose of the relatively unreactive sheets does not gelatinize sulliciently to bond to each other with any degree of strength. The two exterior sheets may be both of the same type -or of different types. If a product of decreased llexibility is desired, a plurality of plies of relatively reactive paper sheets may be substituted for one or more of such single sheets. Again, increasing or decreasing the thickness of the relatively unreactive paper sheets will respectively increase or decrease the flexibility of the end product and'respectively decrease or increase the density and cost of the end product. Generally each sheet will be from 3 to l0 mils thick.

Thus the method of making vulcanized libre in accordance with this invention comprises saturating a plurality of relatively reactive paper sheets, a plurality of relatively unreactive paper sheets, plying the sheets together with at least one. relatively reactive sheet separating each adjacent relatively unreactive sheet, leaching out the said solution and drying the plied sheets.

The terms reactive and unreactive are used herein as a basis of comparison to distinguish the degree of gelatinizing of the cellulose libre when saturated with a gelatinizing agent such as zinc chloride of 65 to 76 Baume or other cellulose gelatinizing agents. The reactive paper sheets employed are formed from libres whose constituent cellulose molecules have an average degree of polymerization of from-500 to about 900 with a minimum alpha cellulose content of 92%. The non-reactive paper will contain cellulose of an average degree of polymerization from 1200 to about 1700. It is to be observed that the level of reactivity of the paper varies generally inversely with the degree of polymerization of the cellulose. As a practical way of estimating .the degree of polymerization of cellulose, the value of the viscosity of cellulose dissolved in some solubilizing agent can be used to calculate the intrinsic viscosity which generally varies inversely with reactivity of the paper. For example, the viscosity determined by the Technical Association of the Pulp and Paper Industry Test, T-230-SM-50 using 0.5 molar cupriethylene diamine for the solution of the cellulose may be used.

The relatively reactive and unreactive papers can readily be formed of any cellulosic libres within the desired ranges of average degree of polymerization by using cellulosic libres which have been processed to yield this property. Highly reactive papers may be formed from properly processed cotton linters, cotton plant libres and rags, and rayon dissolving type wood pulps. Relatively unreactive libre sources are cotton rags and unbleached newsprint pulp, rag pulp and the various types of wood pulps such as groundwood, bleached and unbleached kraft, sullite, semichemical, and soda processed pulp.

As indicated before, the chemical solution to gelatinize cellulose fibres will be preferably zinc chloride with sulfuric acid second choice. Others such as calcium thiocyanate, guanidine and quaternary ammonium hydroxide are effective. While optimum results are normally obtained with a zinc chloride concentration range of 70 to 71 Baume, reactivity will occur with zinc chloride concentrations of 65 to 76 Baume. Similarly, with respect to a sulfuric acid solution, it is preferred to use about 54 Baum but a range of 53 to 56 Baum will effect reactivity.

. desired to insure'rthorough saturation of the sheets with the gelatinizingagent.V The saturated sheets after being plied together are permitted a dwelling time in air before going into the leaching tanks of a minimum of minutes to allow the gelatinized bres to adhere to each other to form a bond between each sheet of paper.

' It isdesirable to have the sulfuric acid in a temperature range of from 45 to 65 F. and the immersion time in the sulfuric acid from 5 to 15 seconds with a subsequent dwelling time in air before going into the leaching tanks of from about 30 lto 60 seconds. Referring again to the drawings, vulcanized fibre in accordance with this invention is produced when sheet 14, 18 and 22 arerof relatively unreactive paper as defined above and sheets 16, and 20 are of relatively reactive paperas defined above, the end Vproduct Will be a sheet 36 as illustrated in FIGURE 2.

Tests of the vulcanized fibre made as previously described demonstrate that various combinations Vof the two papers used for this experiment can be utilized to produce a wide range of excellent grades of vulcanized fibre. The combinationsrof relatively reactive and unreactive cellu-V lose papers can be varied in thicknesses Well as in number of plies in order to vary the properties of the resultant vulcanized fibre.

The invention will be further clarified by the following example. Y

Y EXAMPLE Ik Vulcanized fibreboard of a thickness of 0.029" was made from five rolls of reactive paper sheets and four rolls of unreactive paper sheets having theV characteristics set forth below:

Reactive paper sheets General type of paper Rayon, grade Wood pulp. f Alpha cellulose content 94%'. Average cellulose degree of polymerization 700. Thickness 0.007. Basis Weight (480-24 Yx 36) 40.

i Unreactz've paper sheets Y General type of paper Unbleached kraft. Y Alpha cellulose content 89.5%.

Average cellulose degree of polym- Y' erization 1200.Y Thickness 0.012".

with the sheets being led off the rolls through a tank containing a Baume solution of zinc chloride. The

sheets were passed-through the zinc chloride solutionrin the tank at the rateof'lS per minute remaining in the solution twenty seconds. The sheets were then plied by passing them around an upper roll and a lower roll. After being plied, the'sheets were passed through a series of l2 leaching tanks and the zinc chloride leached out leaving a residual of amam'murn of less than .2% ofrzinc. chloride. The plied sheets were led fromtheterminal leaching tank around drying rolls'and'dried to-aV moisture Acontent of 6% to 8% and subsequently calendered. The

thus treated plied sheets were then wound onto. a storage roll.'l The thus formed vulcanized fibreboard (0.03"

thick) Yhas a tensile (lb/sq. in.) length of 21,000, tensile (lb./sq. in.) cross of 10,550, a flexing count (lengthwise) of 300+ and a flexing count (cross) of What is claimed is: Y

e 1.Y The method of making vulcanized fibre comprising` saturating a plurality of reactive paper sheets having an average cellulose degree of polymerization of from about 500 to about 900 and a minimumV alpha cellulose content of 92% and a plurality of less reactive kraft paper sheets having an average cellulose degree of polymerization of Y from about 1200 to about 1700 with a gelatinizing solution, plying the sheets together with at least one reactive sheet separating each adjacent less reactive sheet, leach-l ing out the said solution and drying the plied sheets.V

2. Ihe method of claim 1 whereinvthe reactive sheets comprise a rayon dissolving pulp.

3. The method of claim 1 wherein the'reactive sheets.

comprise a linters pulp. Y l

4. The method of, claim 1 5. The method of claim 1 wherein the gelatinizing solution l1s a 53 to 56 Baume solution of sulfuric acid.V

l6. Vulcanized fibre comprising a plurality of paper sheets having an average cellulose degree of polymeriza-` tion of from about 500 to about 900 and a'minimurn alpha cellulose content of 92% and a plurality of less reactive kraft paper sheets having -an average cellulose degree of polymerization of from Vabout 1200 to about` References Cited by the Examiner UNITED STATES PATENTS 1,829,157

10/31 VRichter 15e- 76 XR- 1,988,340 1/35 Shoemaker --.15e- 76.

9/41 Robinson 161-269 EARL M. BERGERT, Primary Examiner.

wherein the Vgelatinzing,Y solution is a 65 to 76 Baumsolution of'zincrchloride. 

6. VULCANIZED FIBRE COMPRISING A PLURALITY OF PAPER SHEETS HAVING AN AVERAGE CELLULOSE DEGREE OF POLYMERIZATION OF FROM ABOUT 500 TO ABOUT 900 AND A MINIMUM ALPHA CELLULOSE CONTENT OF 92% AND A PLURALITY OF LESS REACTIVE KRAFT PAPER SHEETS HAVING AN AVERAGE CELLULOSE DEGREE OF POLYMERIZATION OF FROM ABOUT 1200 TO ABOUT 1700, SAID SHEETS BEING PLIED TOGETHER WITH AT LEAST ONE REACTIVE SHEET SEPARATING EACH ADJACENT LESS REACTIVE SHEET AND SAID SHEETS HAVING BEEN REACTED WITH A GELATINIZING SOLUTION. 